Most of them haven't got the slightest clue.

The majority of the millions of pet owners are law abiding, well meaning/adjusted normal people but when it comes to pet keeping, ignorance of their animals' true needs just seems to be the norm. If you explained the shortcomings, most of them would be mortified, but there are no rulings about such issues- its a case of just do what every one else does. Of course nowadays the cages for ferrets, rodents, some small birds etc are often much bigger and fancier than they used to be- a marketing ploy as they cost a lot more to buy- and that does help the inmates to have a somewhat improved life.
Some pet chain stores in the UK now will not sell small-sized hutches for rabbits or guinea pigs, another step in the right direction. The latest publicity on rabbit care says hutches should be of sufficient length to allow 'three hops' and even then a larger attatched run should be an essential, as well as rabbit company. Apparently the simple 'rabbit hutch' was a Victorian innovation for keepng rabbits for a short period before being killed for their meat. That system then got extended into pet rabbit-keeping generally. Again selling larger runs and houses should benefit the pet stores as well as the animals, as the bigger they are, the more expensive they are to buy...
One of my pet(sorry for the pun) dislikes is seeing cluttered bird cages so the birds have no straight lines to fly in to be able to get proper exercise and plastic perches instead of proper wooden ones of varying thickness that suit their feet. Pretty coloured ropes in bird cages too- the birds frequently nibble and then hang themselves in these- they should be banned. Budgies, parakeets and finches shouldn't be kept alone, they are social flock birds. But the saddest sight of all- quite common in some big pet stores as well as in private homes- is large tame Macaws confined to those small metal-barred 'prisons'- these I really hate.